U.S. Pat. No. 4,643,876, incorporated herein by reference, discloses a sterilization system in which an agent such a hydrogen peroxide is introduced into a evacuated sterilizing chamber where it is vaporized and allowed to disperse onto the items to be sterilized. After a desired period of time, electrical energy is applied to the chamber to ionize the gas and form a plasma field at a power level sufficient to achieve sterilization.
This system has been successfully commercialized as the STERRAD.RTM. Sterilization System and is available from Advanced Sterilization Products, Division of Ethicon, Inc., Irvine, Calif. The system is used in hospitals and other environments where it is operated repeatedly throughout the day by personnel having a widely varying range of understanding of the apparatus. To ensure simple and automatic operation with adequate safeguards with respect to human error, the system employs an automated delivery system for delivering the liquid sterilant to the sterilization chamber. Measured portions of the sterilant, in this case hydrogen peroxide but many other sterilizing agents could be substituted therefor, are provided in rupturable cells within a rigid cassette housing. A transport system maneuvers the cassette within the Sterrad.RTM. sterilizer and releases the given quantity of hydrogen peroxide into the sterilization chamber automatically. The cassette and operation of the deliver system are more fully described in the Williams et al. U.S. Pat. Nos. 4,817,800 issued Apr. 4, 1989; 4,913,196 issued Apr. 3, 1990; 4,938,262 issued Jul. 3, 1990; and 4,941,518 issued Jul. 17, 1990, all of which are incorporated herein by reference. In this system, the operator manually grasps the cassette housing and inserts it into the sterilizer. When spent, the cassette is ejected and manually handled by the operator.
This sterilization device with the cassette system offers many advantages. The hydrogen peroxide and plasma kill a wide spectrum of bacteria, viruses, and spores at low temperatures which leave delicate temperature sensitive instruments undamaged. Hydrogen peroxide plasma sterilization meets several environmental and operator safety challenges. After the electromagnetic field producing the plasma is removed, the ionized plasma components recombine to form harmless water and oxygen, avoiding toxic disposal of the sterilant used in the sterilization process. Also, the cassette effectively isolates the operator from the hydrogen peroxide contained therein.
One potential hazard arises from small drops of residual hydrogen peroxide which may be left on the exterior of a spent cassette. A sharp hollow needle pierces the cell which is then pressurized to extract the hydrogen peroxide solution through the needle. In some instances, it is possible for a drop of the solution to escape around the needle and thus remain on the cassette exterior after the extraction process. If an operator's skin or clothing were to contact this droplet, damage could result thereto. Also, operators have been known to accidentally insert a spent cassette into the sterilizer in the mistaken belief that it was actually a new cassette filled with sterilant. Safety mechanisms in the process, such as methods for detecting the presence of sterilant during the sterilization cycle and biological indicators assessing the sterilization cycle efficiency, warn operators of potential cycle failures to prevent inadvertent use of non-sterile instruments thereafter. However, failure of a cycle due to use of a spent cassette entails delays and concomitant expenses.
The present cassette and delivery system encase the cassette within a protective sleeve which isolates the cassette from the operator's hands during all aspects of the cassette handling, thus protecting the operator from contact with any of the sterilant contained therein. Further, an indicator on the sleeve, preferably a moveable label, indicates when the cassette has been used to prevent inadvertent re-use of a spent cassette.